Numbering of video objects and cells

ABSTRACT

A method of recording an encoded bit stream, said encoded bit stream representing a plurality of video objects comprising a sequence of cells together constituting a part of an MPEG2 Program Stream, on a disc like record carrier, such as an optical disc. The method comprises recording video objects comprising a sequence of contiguously recorded cells, each cell comprising a unique cell identification number within a video object, recording of a playback sequence of cells that defines a playable program chain of cells, wherein said sequence comprises references to the cell identification numbers and recording navigation data within said cells comprising said cell identification numbers. 
     The method further comprises dividing at least one previously recorded cell into new cells and/or overwriting at least one previously recorded cell at least partly with a new cell, assigning the at least one new cell with a cell identification number and recording a new playback sequence of cells employing the at least one new cell, the new playback sequence not necessarily employing an incremental numbering of cell identification numbers. 
     Hereby a time consuming renumbering of all cells is being avoided.

FIELD OF THE INVENTION

The invention relates to a method for recording encoded informationsignals as recited in the preamble of claim 1 on a disc like recordcarrier, such as an optically readable disc. The invention furtherrelates to a recording apparatus for performing the method.

BACKGROUND OF THE INVENTION

The DVD-Video format for optically readable discs is defined in the DVDSpecifications for Read-Only Disc, part 3: Video Specifications (version1.0, August 1996). Relevant parts therefrom are being disclosed in forinstance European Patent Application EP 724 264 and U.S. Pat. No.5,784,528, respectively document D1 and D2 in the list of referreddocuments that can be found at the end of this description. Bothdocuments are incorporated by reference herein.

The DVD-Video format as defined in the above mentioned Specificationsfor READ-Only Disc and disclosed in D1 and D2 was created for storingmovies and other video content on read-only DVD media. Some of thefeatures of the DVD-Video format make it less suitable for real-timerecording applications.

However, it is desirable to create and record video streams andassociated data structures on rewritable media in real time which areshould preferably be almost identical to the structures defined in theDVD-Video format. Such rewritable discs should be playback compatiblewith the majority of the installed base of consumer DVD-Video players.The method according to the invention describes a novel and inventiveformat for DVD-Video compatible real-time recording of video streams,referred to hereinafter to as Real Time DVD Video Recording or shortlyDVD-Video Recording. The format defined is intended for home videorecording on an optical medium that is playback compatible withDVD-Video players.

The above-mentioned DVD-Video format demands that data for a VTS beallocated contiguously. This gives all kinds of problems when part ofthe data is overwritten with new recordings.

When editing is performed or part of a title is overwritten, videoobject (VOB) and Cell numbering does not follow the rules of DVD-Videoanymore. The DVD-Video prescribes incremental numbering of video objectsand cells. When recording the disc for the first time that requirementcan generally be met. However, when old recordings are (partly)overwritten, or when the user does editing, it may no be possible tomaintain the incremental numbering. As the VOB and Cell numbering areincorporated in the real time data in the Navigation Packs (NV-PCK), ittakes a lot of time to make the stream correct.

Furthermore, starting within a Cell is not allowed according to the DVDvideo rules.

A Program Chain that defines a play back sequence of Cells, shouldcomprise a Cell start address and a Cell end address. Splitting orpartly overwriting of a Cell leads therefore to new Cells. This has as aconsequence adding a new Cell identification number. As the DVD ReadOnly Video rules requires an incremental Cell and Video Objectnumbering, all Cells and Video Object should be renumbered. Thisrequires a time consuming update of navigation data within the Cells.

OBJECT AND SUMMARY OF THE INVENTION

In consequence, amongst other things, it is an object of the inventionto obviate the above-mentioned disadvantages. According to one of itsaspects a method of recording to the invention is characterized asrecited in the characterizing part of claim 1.

By allowing a non incremental numbering of Cells in a play backsequence, the time consuming update of navigation data within all Cellsis being avoided.

According to a further advantageous aspect of the invention, the methodis characterized as recited in the characterizing part of claim 2.Renumbering of Video Objects is hereby avoided.

Further advantageous aspects of the invention are recited in other,dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further aspects and advantages of the invention will beapparent from and elucidated in more detail hereinafter with referenceto the disclosure of preferred embodiments, in particular with referenceto the appended figures in which,

FIG. 1 illustrates the logical data structure of a DVD disccorresponding to an embodiment for DVD Video Recording according to theinvention;

FIG. 2 illustrates more in detail the structure of the Video Managerarea (VMG) of FIG. 1;

FIG. 3 illustrates more in detail the structure of the Video Title SetInformation area (VTSI) of FIG. 1;

FIG. 4 illustrates the structure of the Video Manager InformationManagement Table (VTSI_(—)MAT) of FIG. 2;

FIG. 5 illustrates the structure of the Program Chain Information area(PGCI);

FIG. 6 shows an example of finding a Titles Program Chain Information(PGCI);

FIG. 7 shows a recording apparatus according to a first embodiment ofthe invention, the respective units therefrom being illustrated in moredetail in the following figures of which

FIG. 8 shows an A/V input unit;

FIG. 9 shows a CODEC unit;

FIG. 10 shows an A/V output unit;

FIG. 11 shows a drive unit, and

FIG. 12 shows a system control unit.

DESCRIPTION OF THE EMBODIMENTS

The data structure to be disclosed hereafter explains the DVD-Videocompatibility behind the Real-Time Video Recording Format and specifieshow it should be used by recorders to create DVD-Video playbackcompatible discs.

To overcome limitations for real-time recording of the DVD-Video formatfor read-only discs, a number of changes have been made to the dataorganization and the use of some of the recording parameters in thereal-time data stream.

The use of Titles and Menus is restricted to improve exchangeability ofrewritable discs between recorders. In addition to this, strict rulesare defined for Play Lists, which can be created by the user to defineplayback sequences of pieces from the recorded Titles.

First a list of definitions is given.

Access Unit

Coded representation of a presentation unit. See ISO/IEC 13818-1 relatedto MPEG-2 systems, document D3 in the list of referred documents thatcan be found at the end of this description, for a more detaileddefinition of MPEG audio and video access units.

Buffer Cell

Last Cell of a Video Object (VOB) containing just one Video Object Unit(VOBU). The Buffer Cell is not used by any Program Chain (PCGC). TheCell ID of a Buffer Cell is equal to 255.

Cell

Sequence of one or more Video Object Units (VOBU). The first VOBU of aCell shall contain video data. Cells are the basic presentation unitsfor the Program Chains (PGC).

Chapter

Subdivision of a Title. Other word for Part_(—)of_(—)Title (PTT).

DVD-VR Format

Short for Video Format Specifications for Real-Time DVD-Video Recording.

DVD-Video Format for Read-Only Discs

Format as specified in the DVD specifications for Read-Only Disc—Part 3:Video Specifications (version 1.0, August 1996), elements of which arebeing disclosed in D1 and D2.

DVD-Video Format for Rewritable Discs

Format of DVD-Video related structures with the modifications specifiedin this disclosure.

Elementary Stream

An elementary stream is a generic term for a sequence of coded video,coded audio, coded graphics or other access units that can be correctlydecoded by a hypothetical decoder operating without special control froman external controller.

Free Space

Recording which is represented by a Free Space Title in the Title SearchPointer Table. If the last Recording is free space, it is notrepresented in this table.

Free Space Title

Full Title or Play List Title which cannot be played back as the relatedProgram Chain Information contains a pre-command to prevent this.Time_(—)Play( ), Time_(—)Search( ), PTT_(—)Play( ) and PTT_(—)Search( )for a Free Space Title are blocked. The Cell information in the ProgramChain of a Free Space Title may not be reliable.

Full Title

Title representing one Recording.

When a Full Title is played, all complete Cells (except the BufferCells) contained in the Recording are played in the order of dataallocation in the VTS Title VOBS. Full Titles may be accessible via theTitle Menu.

Group of Pictures (GOP)

Series of coded pictures starting with a GOP-header followed by an intracoded picture. The GOP represents up to 36 display fields at a rate of59.94 Hz, or 30 fields at a rate of 50 Hz.

MPEG-2 Program Stream (MPEG-2 PS)

Program Stream as defined in ISO/IEC 13818-1 related to MPEG-2 systems,document D3 in the list of referred documents that can be found at theend of this description.

Multiplexed Stream

A multiplexed stream is a single bit-stream, combining one or severalelementary streams that can be played in synchronism.

Play List (or Play List Title)

Title representing a play back sequence of Cells from one Recording.Play Lists are accessible via the Title Menu.

Program Chain (PGC)

Playback sequence of Cells for the presentation of a Menu or a Title.

Real Title

Full Title or Play List Title which is not a Free Space Title.

Recording

Contiguous piece of the VTS Title VOBS, enclosing an integer number ofMPEG-2 PS packs.

The VTS Title VOBS is partitioned into adjacent Recordings which do notnecessarilly coincide with the VOBs in the VOBS.

Title

User accessible unit listed in the Title Search Pointer Table.

Title Menu

Menu which gives the user access to Play Lists and optionally to FullTitles.

Title Search Pointer Table

Table in the Video Manager listing all available Play Lists and FullTitles on the disc. It is a starting point for finding the data which isrelevant for playing back a Title.

Video Manager (VMG)

DVD-Video data structures containing information about the recordedvideo data and the Title Menu. The Title Search Pointer Table is one ofthe elements of the Video Manager.

Video Object (VOB)

A Video Object is (a part of) a sequence of contiguously recorded Cells,together constituting (a part of) an MPEG-2 Program Stream.

An integer number of MPEG-2 Program Stream packs may be missing from thebeginning of the first Cell of the VOB, if this Cell is not used by anyTitle. The last Cell of a VOB is a Buffer Cell.

A VOB shall contain one video elementary stream. Gaps in the videostream are allowed under conditions specified by the DVD-Videospecifications.

According to the DVD-Video specifications a VOB may also contain up toeight Audio streams (in elementary audio streams and/or in privatestreams) and up to 32 Sub-picture streams. The DVD-VR format only allowsone Audio stream and one Sub-picture stream within the same VOB.

Video Object Unit (VOBU)

Integer number of MPEG-2 Program Stream packs representing apresentation period between 0.4 and 1.0 seconds.

The last VOBU of a Cell has a maximum presentation period of 1.2seconds. When the VOBU contains Video, the video data consists of aninteger number of GOPs and starts with a sequence header, a GOP headerand an intra coded picture.

A Sub-picture Unit is optional in a VOBU and cannot cross VOBUboundaries. The SPU's associated validity period ends at or before theend presentation time of the VOBU.

Video Object Set (VOBS)

Collection of contiguously recorded VOBs.

VOBs which are used for the menus are stored in the Video Manager VOBS(VMGM_(—)VOBS). VOBs which are used for the Titles are stored in the VTSTitle VOBS (VTSTT_(—)VOBS).

FIG. 1 shows the general data structure in accordance with the Real-TimeVideo Recording format. The data structure comprises a Lead-In area(LI), a Volume (VOL) and File System area (FS), a Video Manager area(VMG), one Video Title Set (VTS), an area reserved for other structures(OTHER) and a Lead-Out area (LO) as known from the DVD-ROM datastructure. Not specifically shown in FIG. 1 is Presentation ControlInformation (PCI) and Data Search Information (DSI) within the VideoObject Set for VTS Titles (VTSTT_(—)VOBS), both dispersed in theNavigation Packs (NV_(—)PCK) of each Video Object Unit (VOBU).

The data organization according to the Real-Time Video Recording formatwill first be discussed in general.

With respect to the Video Manager (VMG) the following is remarked. TheVideo Manager (VMG) shall contain a Title Menu. Consequently a VideoObject Set for Video Manager Menu (VMGM_(—)VOBS) is mandatory.

With respect to the Video Title Sets (VTS) the following is remarked.The data structure on a disc contains only one Video Title Set (VTS).The Root Menu shall contain a dummy Program Chain (PGC) with apre-command calling the Title Menu. No other Video Title Set (VTS) menusshall be present on the disc. Consequently the Video Title Set (VTS)does not contain a Video Object Set for a Video Title Set Menu(VTSM_(—)VOBS). The Video Object Set for Video Title Set Titles(VTSTT_(—)VOBS) of the Video Title Set (VTS) contains the recorded videocontent.

With respect to the Video Object Set (VOBS), the Video Objects (VOBs)and Cells, the following is remarked. A Video Object (VOB) is (a partof) a sequence of contiguously recorded Cells, together constituting (apart of) an MPEG-2 Program Stream as defined in D4. An integer number ofMPEG-2 Program Stream packs may be missing from the beginning of thefirst Cell of the Video Object (VOB), if this Cell is not used by anyTitle. The last Cell of a Video Object (VOB) is a Buffer Cell, which isnot used by any Title. A Video Object Set (VOBS) is a collection ofcontiguously recorded Video Objects (VOBs). Video Objects (VOBs) andCells on a rewritable disc are not fully compliant with the VideoSpecifications for the DVD Read-Only Disc as disclosed in D2 and D4. Thefollowing exceptions are allowed or required.

-   1) The DVD-Video specification demands that a Video Object (VOB)    starts with an System Clock Reference (SCR) equal to zero. This is    not required for DVD-VR discs.-   2) The Display of the video stream from one Video Object (VOB) does    not have to start with a top field nor have to end with a bottom    field.-   3) The DVD-Video specification prescribes incremental numbering of    Video Objects (VOBs) and Cells. When recording the disc for the    first time that requirement can generally be met. However, when old    recordings are (partly) overwritten, or when editing is done by the    user, it may not be possible to maintain the incremental numbering.    To overcome this problem, DVD-VR format requires that the Video    Object Identification number (VOB ID) of all Video Object (VOBs) is    equal to ‘1’. In addition to this, Cell ID numbers (except    number 255) remain unique but they are allowed to be non sequential.-   4) Video Objects (VOBs) and Cells contain Navigation packs    (NV_(—)PCK) with forward references to facilitate forward search.    Some of these forward references cannot be known at recording time    and therefore must be encoded with values which make legacy playback    devices behave in an acceptable way.-   5) The Navigation packs (NV_(—)PCK) also contain a parameter    specifying the presentation termination time of the last video frame    of the Video Object (VOB). This parameter cannot be made correct in    real time in all cases. To solve this problem a high number will be    recorded for this parameter. A Buffer Cell at the end of a Video    Object (VOB) guarantees that the end of a Video Object (VOB) is    never reached during play back.

With respect to recordings, the following is remarked. The Video ObjectSet for Titles in a Video Title Set (VTSTT_(—)VOBS) can be partitionedinto a collection of adjacent pieces, called Recordings, which do notnecessarily coincide with the Video Objects (VOBs). Recordings enclosean integer number of MPEG-2 PS packs.

Recordings relate to the partitioning of the content as it is presentedto the user.

With respect to Full Titles, Play Lists and Free Space, the following isremarked. For each Recording two One_(—)Sequential_(—)PGC_(—)Titles arecreated: one Full Title and one Play List. The Full Title defines playback of all complete Cells (except Buffer Cells) of a Recording in theorder of allocation in the Video Object Set (VOBS). The Play List may bedifferent from the Full Title. If so it defines play back of a subset ofthe Cells which are played by the Full Title.

Full Titles and Play Lists are each represented as a Title in the TitleSearch Pointer Table in VMGI (TT_(—)SRPT) and as a Title Unit (TTU) inthe Part_(—)of_(—)Title Search Pointer Table in the VTSI(VTS_(—)PTT_(—)SRPT). A Play List points to the same Program Chain (PGC)as the corresponding Full Title, unless a different Program Chain (PGC)is recorded for the Play List.

Full Titles and Play List Titles are Real Titles, unless they are taggedas Free Space. When a Full Title is deleted by the user, both the FullTitle and the Play List in the Title Search Pointer Table (TT_(—)SRPT)are tagged as Free Space by setting a unique Playback Type value(TT_(—)PB_(—)TY). If two consecutive Full Titles are deleted, theentries in the Title Search Pointer Table (TT_(—)SRPT) shall be combinedinto one new Title. Also the related Play Lists are combined and taggedas Free Space. Free space that is available on the disc at the end ofthe VTS Title VOBS or beyond the boundaries of the VTS, is not reflectedin the TT_(—)SRPT. FIG. 5 illustrates an example of finding a Title'sPGCI.

Within FIG. 5 the following data structures are given: Title Play BackType (TT_(—)PB-TY), Number of Part_(—)of_(—)Title (PTT_(—)Ns), VTS TitleNumber (VTS_(—)TTN), PGC_(—)Number (PGCN), Program Number (PGN), VTSTitle Number (VTS_(—)TTN), Start Address of VTS Program ChainInformation Table (VTS_(—)PGCI-SA), Program Chain Information Table(PGCIT), Number of Angles (AGL-Ns), Parent_(—)ID_(—)field for Title(TT_(—)PTL_(—)ID-FLD), VTS Number (VTSN) and Parent ID-field(PTL_(—)ID_(—)FLD).

Each Title (except for the last Play List Title and the last Full Title)is linked to the next Title by a LinkPGCN instruction in the associatedProgram Chain Information (PGCI). The Program Chain Information (PGCI)of the last Play List and the last Full Title contains a CallSS to theTitle Menu. If the Title is tagged as Free Space, this instruction isstored as a pre-command in the Program Chain Information (PGCI).Otherwise the instruction is stored as a post-command.

The number of Full Titles on a DVD-VR disc is equal to the number ofPlay Lists with a maximum of 49. Titles can be sub-divided into amaximum of 99 Chapters (Part_(—)of_(—)Titles). The maximum number ofChapters for all Full Titles on one disc is 254.

In the following the restrictions and modifications compared to theread-only format will be given.

As already disclosed with reference to FIG. 1, exactly Video Title Setis recorded on disc. FIG. 2 illustrates the data structure of VideoManager General Information (VMGI) within the Video Manager (VMG) areaas shown in FIG. 1. As in FIG. 1, the Presentation Control Information(PCI) and Data Search Information (DSI) are not shown in FIG. 2,although this information is dispersed in corresponding Navigation Packs(NV_(—)PCK) in each Video Object Unit (VOBU) of the Video Object Set forthe Video Manager Menu (VMGM_(—)VOBS).

With respect to the Video Manager Information Management Table(VMGI_(—)MAT), the first 8 bytes of the Provider Unique ID (PVR_(—)ID)contains the string ‘DVD-VR01’. The First Play Program Chain (FP_(—)PGC)contains just a JumpSS to the Title Menu as a pre-command.

The Title Search Pointer Table (TT_(—)SRPT) consists of two sections ofequal length. The first half contains pointers for N Play Lists and thesecond half contains pointers to N Full Titles. Play Lists as well asFull Titles are sorted in the order of incrementing start addresses ofthe first used Cell in the Video Object Set (VOBS). All Titles areOne_(—)Sequential_(—)PGC_(—)Titles for which Time_(—)Play( ) andTime_(—)Search( ) are blocked. Part_(—)of_(—)Title_(—)Play( ) andPart_(—)of_(—)Title Search( ) shall be blocked for Titles which areassociated with Free Space and shall not be blocked for other Titles.Table 1 lists allowed Playback Types as indicated by theTitle_(—)Playback_(—)Type (TT_(—)PB_(—)TY) field.

TABLE 1 Allowed values of TT_(—)PB_(—)TY Value of TT_(—)PB_(—)TY Type ofTitle 0000 0101b Real Title which is not the last Play List or not thelast Full Title 0001 0101b Real Title which is the last Play List or thelast Full Title 0000 0111b Free Space Title

The Video Manager Menu Program Chain Information Unit Table(VMGM_(—)PGCI_(—)UT) is just linked to the Title Menu. There shall beonly one Language Unit. The Video Manager Menu exists in this LanguageUnit.

Following the Video Title Set Attribute Table (VTS_(—)ATRT), the VideoManager Menu Cell Address Table (VMGM_(—)C_(—)ADT) is restricted to amaximum of 170 cells and the Video Manager Menu Video Object UnitAddress Map (VMGM_(—)VOBU_(—)ADMAP) to a maximum of 511 VOBUs. Theremaining part of the Video Manager area (VMG) is occupied with theVideo Manager Menu Video Object Set (VMGM_(—)VOBS) and the back up ofthe Video Manager Information (VMGI_(—)BUP).

With reference to FIG. 3, the Video Title Set Information (VTSI) will bediscussed. As the Root Menu contains just a dummy Program Chain (PGC)and other menus are not allowed, the Video Titel Set (VTS) Menus have noassociated Video Object (VOB) data. Consequently the Cell Address Tableof the Video Title Set Menu (VTSM_(—)C_(—)ADT) and the Address Map ofthe Video Object Unit of the Video Title Set (VTSM_(—)VOBU_(—)ADMAP) donot exist.

The Management Table of the Video Title Set Information (VTSI_(—)MAT)comprises the following area (not shown in the figure):

-   -   the VTS Video Attributes (VTS_(—)V_(—)ATR) (the video        compression mode complies with MPEG-2),    -   the number of Audio Streams (VTS_(—)AST_(—)Ns) describing the        number of different audio stream attribute sets used in this        VTS,    -   the VTS Audio Stream Attribute Table (VTS_(—)AST_(—)ATRT)        listing the different audio stream attribute sets which are        defined (and may or may not be used) for this VTS. The PGCI for        each Title defines which of the sets is actually used,    -   the number of Sub-picture Streams (VTS_(—)SPST_(—)Ns) (set to        one in this VTS) and    -   the VTS Sub-picture Stream Attribute Table (VTS_(—)SPST_(—)ATRT)        (all fields in this table are zero)

The Video Title Set Information (VTSI) further comprises further a VideoTitle Set Part_(—)of_(—)Title Search Pointer Table (VTS_(—)PTT_(—)SRPT)wherein the Title Units are recorded in the same order as Titles inTitle Search Pointer (TT_(—)SRPT).

Next is present a Video Title Set Program Chain Information Table(VTS_(—)PGCIT). The number of Video Title Set Program Chain Information(VTS_(—)PGCI) search pointers is equal to the number of Titles in TitleSearch Pointer Table (TT_(—)SRPT). The search pointers are recorded inthe same order as the Titles. All Program Chains (PGCs) are Entry PGCswith all bits zero for Block mode, Block type and Parental ID Field(PTL_(—)ID_(—)FLD). When a Play List is equal to the associated FullTitle, their Start Address of Video Title Set Program Chain Information(VTS_(—)PGCI_(—)SA) values are identical.

With respect to the Video Title Set Menu Program Chain Information UnitTable (VTSM_(—)PGCI_(—)UT) the following is remarked. The number ofVideo Title Set Menu Language Units as specified in VTSM_(—)PGCI_(—)UTIshall be 1. There is exactly one Video Title Set Menu Language UnitSearch Pointer (VTSM_(—)LU_(—)SRP). The Video Title Set Menu Existencefield (VTSM_(—)EXST) shall contain the value (1000 0000b) to indicatethat just the Root Menu exists. The Video Title Set Menu Language Unit(VTSM_(—)LU) contains just one Program Chain Information Search Pointer(VTSM_(—)PGCI_(—)SRP). The Video Title Set Menu Program Chain Categoryparameter (VTSM_(—)PGC_(—)CAT) for the Video Title Set Menu ProgramChain (VTSM_(—)PGC) contains the value (8300 0000h) indicating that theassociated Program Chain (PGC) is the Entry PGC for the Root Menu. Thereis exactly one Video Title Set Menu Program Chain Information(VTSM_(—)PGCI).

The Video Title Set Time Map Table (VTS_(—)TMAPT) contains Video TitleSet Time Maps (VTS_(—)TMAPs) that are present for all Titles on the discbut do not contain any map entries.

With respect the Video Title Set Cell Address Table (VTS_(—)C_(—)ADT),the parameter contains the number of Video Object in the Video Title Set(VTS_(—)VOB_(—)Ns) contains the contains the value ‘1’. It is noted thatthe VTS_(—)VOB_(—)Ns does not reflect the actual number of VOBs in theVideo Object Set of a rewritable disc. It is set to 1 as the VOB IDnumber of all VOBs is set to ‘1’. All Video Title Set Cell PieceInformation (VTS_(—)CPI) have the same value (‘1’) for the Video TitleSet Video Object ID Number (VTS_(—)VOB_(—)IDN). Exactly 254 VTS_(—)CPIblocks are recorded with VTS_(—)C_(—)IDN starting from ‘1’ andincrementing up to and including ‘254’. The Start Address and EndAddress of the Video Title Set Cell Piece (VTS_(—)CP_(—)SA andVTS_(—)CP_(—)EA) of Cell Pieces which are not referenced by any PGC of aReal Title contain the value (0000 0000h). It is noted that Cell Piecesthat are referenced by a PGC of a Free Space Title contain zero startand end addresses.

With respect to The Video Title Set Video Object Unit Address Map(VTS_(—)VOBU_(—)ADMAP) it is remarked that all Video Object Unit (VOBU)start addresses of the VOBUs which are completely contained inVTSTT_(—)VOBS are listed here in ascending order. It is noted that VOBUstart addresses of VOBUs which are part of Free Space are also includedin the VTS VOBU Address Map.

Next the structure of the Program Chain Information area (PGCI) forTitle Program Chains will be given with reference to FIG. 5. Thisstructure comprises a Program Chain General Information Area (PGC-GI), aProgram Chain Command Table (PGC_(—)CMDT), a Cell Playback InformationTable (C_(—)PBIT) and a Cell Position Information Table (C_(—)POSIT).

With respect to the Program Chain General Information (PGC-GI) it isnoted that exactly one of the Availability flags in the Program ChainAudio Stream Control Table (PGC_(—)AST_(—)CTLT) is set to (1b). When thei^(th) Availability flag is set, the i^(th) Audio stream parameter setdefined for this Video Title Set (VTS) is valid for this Program Chain(PGC). The Decoding Audio stream number is always ‘0’.

The availability flag of the first Program Chain Sub-picture StreamControl (PGC_(—)SPST_(—)CTL) field in the Program Sub-picture StreamControl Table (PGC_(—)SPST_(—)CTLT) is set to (1b). All other bits ofthe Program Sub-picture Stream Control Table (PGC_(—)SPST_(—)CTLT)contain the value (0b).

The Program (PG) Playback mode in the Program Chain Navigation Control(PGC_(—)NV_(—)CTL) is set to sequential playback. The Still time valueis set to no Still.

The PGC Command Table (PGC-CMDT) contains exactly three commands.According to this version of the specification only one command isactually used (for Title linking), the other two commands are NOPcommands (0000 0000h). Which command is used for Title linking isdefined in Table 2.

TABLE 2 Commands in PGCI PGC associated with . . . contains . . . as a .. . Real Title which is not the last Play List LinkPGCN post-command ornot the last Full Title in TT_(—)SRPT to PGC of next Real Title RealTitle which is the last Play List or CallSS post-command the last FullTitle in TT_(—)SRPT to Title Menu Free Space Title LinkPGCN pre-commandto PGC of next Real Title

With respect to Cell Playback Information Table (C_(—)PBIT): Cells arenot part of an Angle Block and do not exist in an Interleaved Block.

With respect to the Cell Position Information Table (C_(—)POSIT): theIdentification Numbers of the Video Objects of all Cells in the PGCcontain the value ‘1’. It is noted that, on DVD-VR discs, all VOBs havethe same VOB_(—)IDN.

It is allowed that the Cell ID number of a Cell of which the Seamlessplayback flag set in Cell Playback Information, is not the same as theprevious Cell ID number incremented by 1.

With respect to the Presentation Control Information (PCI) it is notedthat modifying a Play List may require that a Cell is split into two newCells. In that case all values of Cell Elapse Time (C_(—)ELTM inPCI_(—)GI) shall be updated in all PCI fields in the second Cell.

Additional data fields with respect to the DVD-Video format forRead-Only discs for carrying real-time stream attributes are givenbelow.

The last reserved 32 bytes of the General Information of PresentationControl Information (PCI_(—)GI) are redefined in this specification asshown in table 3

TABLE 3 Redefinition of reserved fields at end of PCI_(—)GI Number ofContents bytes Reserved reserved 16 bytes (8) PCI_(—)GI_(—)XI PCI_(—)GIExtension Information 1 byte (9) RT_(—)V_(—)ATR Video Attributes 1 byte(10) RT_(—)AST_(—)ATR Audio Stream Attributes 1 byte Reserved reserved13 bytes Total 32 bytes

PCI_(—)GI_(—)XI identifies the application and specifies the length ofthe extension. If all bits in this byte are zero, also the bytes ofPCI_(—)GI following this field are zero:

b7 b6 b5 b4 b3 b2 b1 b0 Application Identifier Extension Length

Application Identifier contains the value (0001b) if the streamattributes as defined in VTSI_(—)MAT for this VTS must be overruled bythe real-time stream attributes. Otherwise contains the value (0000b).The real-time stream attributes are valid from Start PTM until End PTMof the VOBU in which this field is contained.

Extension Length defines the number of bytes for this extensionfollowing this field. It shall contain the value (0010b) if ApplicationIdentifier is (0001b). It contains the value (0000b) if ApplicationIdentifier is (0000b).

RT_(—)V_(—)ATR describes the real-time Video stream attributes.

b7 b6 b5 b4 b3 b2 b1 b0 Aspect reserved reserved Source reserved FilmRatio picture camera letter mode boxed

Aspect ratio, Source picture letterboxed and Film camera mode havemeanings as defined in the DVD specifications for the Read_(—)Only Disc.

RS_(—)AST_(—)ATR describes the real-time Audio stream attributes:

b7 b6 b5 b4 b3 b2 b1 b0 reserved Surround reserved Type

Surround Type as defined in the DVD Specifications of the Read-OnlyDisc.

With respect to Data Search Information (DSI) it is noted that all VOBsare allocated in Contiguous Blocks and there are no Angles.

With respect to the Data Search Information General Information(DSI_(—)GI) it is remarked that the Video Object ID number (VOB ID)number is always 1. Further there is no requirement that the Cell IDnumbers are monotonically increasing from 1 in the Video Object. Thefollowing rules shall be applied for Cell ID:

-   -   Cell ID is identical in all VOBUs belonging to the same Cell    -   Cells which are used by Real Titles are uniquely identified by        their Cell ID

It is noted that modifying a Play List may require that a Cell is splitinto two new Cells. In that case all values of Cell Elapse Time(C_(—)ELTM in DSI_(—)GI) shall be updated in all DSI fields in thesecond Cell.

With respect to Video Object, it is remarked that an integer number ofMPEG-2 Program Stream packs may be missing from the beginning of thefirst Cell of the VOB, if this Cell is not used by any Title. The lastCell of a VOB is a Buffer Cell.

It is noted that seamless connections between VOBs are excluded.

Only one Audio stream is allowed within a VOB. The Audio decoding streamnumber is ‘0’.

Only one Sub-picture stream is allowed within a VOB. The Sub-picturedecoding stream number is ‘0’. Data for a Sub-picture Unit (SPU) isfully contained in one VOBU. The SPU validity period shall not startbefore the Start PTM of the VOBU, nor shall it end later than the EndPTM of the VOBU.

The DVD-Video format for rewritable discs is not fully identical to theDVD-Video format for read-only discs. The differences are (1) in therules for data allocation and (2) in some details of the navigation datain the real-time data streams. The first kind of differences generallyhas no consequences for DVD-Video players. As a consequence of thesecond kind of differences in some cases trick mode behaviour ofDVD-Video playback devices with rewritable discs may not be alwaysexactly the same as with prerecorded discs. Manufacturers can improvecompatibility between DVD-Video players and rewritable discs byfollowing the guidelines given in the next.

With respect to VOBS Structures:

On rewritable DVD-Video discs some rules for the Video Object Set datastructures are different from the rules for read-only discs. DVD-Videoplayers will play back rewritable discs well when they are robustagainst:

-   -   non-sequential numbering of VOBs in the VTSTT_(—)VOBS    -   non-sequential numbering of Cells within a VOB    -   the existence of remnants of partly overwritten Cells or other        unused data in between “active” Cells    -   modified rules for forward search pointers as defined next:

DVD-Video recorders are required to at least fill in correct forwardpointers FWDI(n) for n≦M. Forward pointers FWDI(n) with M<n≦N containthe last correct value. For n>N forward pointers point to the end of thecurrent Cell. The duration of a Cell on a rewritable disc is typically60 seconds.

This means that for forward search functionality DVD-Video players canstill rely on the FWDI pointers for the lower speeds (2×, 4×, 8×). Forhigher speeds, the player can still use the long distance FWDI pointersbut in this case they point to the end of the current Cell. If accuratefast search speeds are desired, the speed can be adjusted by picking upintermediate pictures (e.g. by applying a FWDI(6) pointer) or byadapting the display period of the pictures.

FIG. 7 shows a recording apparatus according to a first embodiment ofthe invention. The recording apparatus is composed of several units. Oneunit is the A/V input unit 1. The A/V input unit 1 receives image andsound signals at antenna input terminal 2 and an external sound/imageinput terminal 3. The antenna input terminal 2 is adapted to receivebroadcasted modulated A/V signals transmitted by either satellite,terrestrial or cable source. The external sound/image input terminal 3is adapted to receive a non modulated audio signal or a non-modulatedvideo signals generated directly by respectively an audio or a videosource.

FIG. 8 illustrates the A/V input unit 1 in more detail. A tuner 5, whichis connected to the antenna input terminal 2, demodulates the modulatedA/V antenna signals and outputs the demodulated signals to a suitableA/V demultiplexing unit 6 for separating audio signals from videosignals. An audio A/D converter unit 7 outputs a digital audio signal Aand a NTSC/PAL/SECAM decoding unit 8, comprising a video A/D converter,outputs a digital video signal V. These signals A and V are outputted toa encoding/decoding unit 9, which is illustrated in more detail in FIG.9. The encoding/decoding unit 9 compresses and encodes the signals A andV, respectively by an audio encoder 10 and a video encoder 11, convertsthem to a multiplexed and compressed stream conforming to VideoRecording specifications, employing a multiplexer 12. To this purposesthe audio encoder 10 and video encoder 11 are adapted to perform sourcecompression according to a specific standard for compression, such asfor example MPEG-2 for audio and video.

The compressed and multiplexed stream is submitted via a track buffer13, which absorbs rate fluctuations stemming from intermittent recordingand data reproduction from a disc, to a drive unit 14. The encoding/anddecoding unit 9 also expands a compressed stream read from a recordingmedium by the drive unit 14 and outputs separately an audio signal A anda video signal V to the A/V output unit 15. To this purpose, theencoding/decoding unit 9 comprises a suitable A/V decoder 16 fordecoding the compressed audio and video source signals.

The A/V output unit 15, which is illustrated in more detail in FIG. 10,comprises an audio D/A converter 17 for outputting sound signals to anexternal sound output terminal 18. The A/V output unit 15 furthercomprises a video encoder—D/A converter unit 19 for outputting videosignals to an external image output terminal 20.

FIG. 11 illustrates the drive unit 14 in more detail. This unit 14receives the compressed stream generated by the encoding/decoding unit9, and adds an error-correction code by a suitable error correctionprocessing unit 21 to the stream. Next a channel modulation/demodulationunit 22 converts the stream with error-correction code to channel bitsadapted for recording on a recording medium 23. In case of a DVD-discthe EFM+ modulation scheme is being applied. Recording and reading incase of a recording medium 23 of the optical type, is performed by alaser comprised in an optical head unit 25. A laser power control unit24 is controlling the laser. Reflected signals from the recording medium23 are being converted by an amplifier and waveform equalizer circuit 26into two-value signals. The resultant compressed stream is furtherdemodulated by the modulating/demodulation unit 22, error corrected bythe error correction processing unit 21 and outputted to theencoding/decoding unit 9 via track buffer 13.

A servo circuit 27, connected to the amplifier and waveform equalizercircuit 26, controls the positioning of the optical head unit 25relative to the recording medium 23 and the rotational velocity of therecording medium 23 by controlling rotational driving means 28.

A system control unit 29, as shown in FIG. 12, controls each block andperform file control, control information management and track buffercontrol. To this purpose a system control processing unit 30 is providedthat is being connected to memory means 31 loaded with a suitableoperation system. Operator input means 32 and operator output means 33are connected to the memory means 31. The operator input means 32comprising for instance keying means and the operator output meanscomprising display means.

Although the invention has been described with reference to preferredembodiments thereof, it is to be understood that these are notlimitative examples. Thus, various modifications thereof may becomeapparent to those skilled in the art, without departing from the scopeof the invention, as defined by the claims. The invention can beimplemented by means of both hardware and software, and that several“means” may be represented by the same item of hardware. Further, theinvention lies in each and every novel feature or combination offeatures. It is also remarked that the word ‘comprising’ does notexclude the presence of other elements or steps than those listed in aclaim. Any reference signs do not limit the scope of the claims.

LIST OF REFERRED DOCUMENTS

-   (D1) European Patent Application EP 724 264-   (D2) U.S. Pat. No. 5,784,528-   (D3) ISO/IEC 13818-1: 1995 Information Technology—Generic Coding of    moving pictures and associated audio information: Part 1: Systems    (MPEG2-systems)

1. A method of recording an encoded bit stream, said encoded bit streamrepresenting a plurality of video objects comprising a sequence of cellstogether constituting a part of an MPEG2 Program Stream, on a disc likerecord carrier, such as an optical disc, said method comprising:recording video objects comprising a sequence of contiguously recordedcells, each cell comprising a unique cell identification number within avideo object; recording a playback sequence of cells that defines aplayable program chain of cells, wherein said sequence comprisesreferences to the cell identification numbers, recording navigation datawithin said cells comprising said cell identification numbers,characterized by, dividing at least one previously recorded cell intonew cells and/or overwriting at least one previously recorded cell atleast partly with a new cell, assigning the at least one new cell with acell identification number, recording a new playback sequence of cellsemploying the at least one new cell, the new playback sequence notnecessarily employing an incremental numbering of cell identificationnumbers.
 2. A method according to claim 1, characterized by, assigningall video objects the same video object identification number.
 3. Amethod according to claim 2, wherein said assigning of new cells withcell identification numbers comprise updating the navigation data withinthe new cells.
 4. A method according to claim 3, wherein said updatingcomprises updating a cell elapse time and a cell identification number.5. A method according to claim 4, wherein a cell, video object, aplayback sequence, a cell identification number, navigation datacorresponds respectively to a Cell, a Video Object (VOB), a ProgramChain (PGC), a Cell ID number and a Navigation Pack (NV-PCK) of the DVDRead Only Video Specification.
 6. A recording apparatus for recording anencoded bit stream, representing a plurality of video objects comprisinga sequence of cells together constituting a part of an MPEG2 ProgramStream, on a disc like record carrier, such as an optical disc, therecording apparatus comprises recording means adapted to record, asequence of contiguously recorded cells, each cell comprising a uniquecell identification number within a video object, a playback sequence ofcells that defines a playable program chain of cells, wherein saidsequence comprises references to the cell identification numbers,navigation data within said cells comprising said cell identificationnumbers, characterized in that, the recording apparatus comprises systemcontrol means adapted to control the recording means to to divide atleast one previously recorded cell into new cells and/to overwrite atleast one previously recorded cell at least partly with a new cell, toassign the at least one new cell with a cell identification number, torecord a new playback sequence of cells employing the at least one newcell, the new playback sequence not necessarily employing an incrementalnumbering of cell identification numbers.
 7. A recording apparatusaccording to claim 6, characterized in that, the system control meansare adapted to assign all video objects the same video objectidentification number.
 8. A recording apparatus according to claim 7,characterized in that, the system control means are adapted to updatethe navigation data within the new cells.
 9. A recording apparatusaccording to claim 8, characterized in that, the system control meansare adapted to update a cell elapse time and a cell identificationnumber.
 10. A recording apparatus according to claim 9 wherein a cell,video object, a playback sequence, a cell identification number,navigation data corresponds respectively to a Cell, a Video Object(VOB), a Program Chain (PGC), a Cell ID number and a Navigation Pack(NV-PCK) of the DVD Read Only Video Specification.
 11. A method ofrecording an encoded bit stream representing a plurality of videoobjects constituting a part of an MPEG2 Program Stream, by recordingvideo objects as a sequence of contiguously recorded cells, with eachcell having a unique cell identification number within a video object,recording a playback sequence of cells that defines a playable programchain of cells, wherein said sequence comprises references to the cellidentification numbers, recording navigation data within said cellsusing said cell identification numbers, characterized by: dividing atleast one previously recorded cell into new cells; overwriting at leastone previously recorded cell at least partly with a new cell; assigningthe at least one new cell with a cell identification number; andrecording a new playback sequence of cells employing the at least onenew cell.
 12. The method according to claim 11, characterized by:assigning all video objects the same video object identification number.13. The method according to claim 11, wherein said assigning of newcells with cell identification numbers comprise updating the navigationdata within the new cells.
 14. The method according to claim 13, whereinsaid updating comprises updating a cell elapse time and a cellidentification number.
 15. The method according to claim 11, wherein acell, a video object, a playback sequence, a cell identification number,navigation data corresponds respectively to a Cell, a Video Object, aProgram Chain, a Cell ID number and a Navigation Pack are as stated witha DVD Read Only Video Specification.
 16. The method according to claim11, wherein recording the new playback sequence does not employ anincremental numbering of cell identification numbers.
 17. The methodaccording to claim 11, wherein recording the new playback sequenceemploys an incremental numbering of cell identification numbers.